This invention relates to an oil-sealed vacuum pump which includes an externally arranged oil circuit communicating with the pump by means of two ports and a filter assembly which is situated externally of the vacuum pump and which may be operatively connected to or disconnected from the oil circuit by a coupling device.
It is advisable to provide a mechanical vacuum pump, for example, a rotary vane pump or a rotary plunger pump with an oil filter if there are risks of a substantial soiling of the pump oil by solid particles such as dust. In case the pump is used in connection with chemicals, the use of a chemical oil filter is of particular importance to prevent corrosion of the pump by acid vapors. Conventionally, the filter arrangement in the oil circuit is such that a replacement of the filter elements can be effected only after the vacuum pump is brought to a standstill.
It is, however, often a desideratum to run vacuum pumps continuously over substantially extended periods. To make possible filter replacement while the pump is running, the oil circuit is conventionally arranged externally of the pump and the two parts which maintain communication between the pump and the oil circuit are each connected with a part of a hose coupling. Communication with the filter assembly is effected by two hoses each having the counterpart of the hose coupling and completing the oil circuit of the vacuum pump through the filter assembly. Prior to replacing a filter element, the hose couplings are disconnected and simultaneously, a blocking of the hoses and the ports of the oil circuit at the pump side is effected. Thereafter, a replacement of the filter or filter element may take place. The oil circuit at the pump side has to be short-circuited in order to prevent the build-up of an excessive pressure in the oil circuit due to the continuing run of the pump. Such short-circuiting is conventionally effected by a pressure relief valve which is situated at the pump side in the vicinity of the circuit ports.
The above-outlined conventional arrangement is disadvantageous in that hose couplings are used which, due to their relatively complex construction are prone to malfunction. The two hose couplings form, in essence, four coil spring-biased valves whose components are, during normal operation, exposed directly to the oil stream which may be carrying corrosive impurities. Risks of damage to the springs are particularly high. In case the springs are not able to function properly during the filter element replacement (that is, they are not capable of producing a sufficient closing force), the hot, soiled or even poisonous liquid pump sealant (oil) may escape.
Further, the functioning of the check valve required in the prior art construction is endangered to a degree proportionate to the impurities. In case the check valve does not open during filter replacement because of an excessive soiling, impermissible pressure increases and resulting oil conduit breaks are unavoidable. If, on the other hand, the check valve remains open after filter element replacement, a sufficient purification of the oil is no longer performed.